The main objective of these studies is to define the cellular and molecular basis of changes in the regulatory auto-anti-idiotypic antibody network with aging. It was found in preliminary studies that the magnitude of the auto-anti-idiotypic antibody production arising during the downward regulation of an immune response increases with age. The first aspect of the project will involve the determination of the kinetics and magnitude of the auto-anti-idiotypic antibody response following immunization with thymus-independent and dependent antigens. The second phase will involve the identification of the cellular basis of the deregulation of the immune network. The third phase will involve the analysis of the repertoire of antibody expression following an antigen stimulation in immunized mice of different ages using auto-anti-idiotypic antibody as a probe.